Electric iower plant



Oct. 12, 1937. L. c. FRANK I ELECTRIC POWER PLANT Filed Oct. 5, 1935INVENTOR L 60 6. Frank.

Patented Oct. 12, 1937 PATENT OFFICE ELECTRIC IOWEB PLANT Leo C. Frank,Irwin, Pa

assimito Westinghouse Electric &' Manufacturing Company,

East Pittsburgh, Pa., syivania Application October 3,

14 Claims.

My invention relates, generally, to electric power plants, and, moreparticularly, to enginegenerator systems for supplying power to variableloads such, for example, as arc searchlights and 6 the remote controland sound locator apparatus therefor.

In the operation of searchlights and sound-locator control equipment, itis necessary to provide for supplying power to operate the sound- 10locator equipment and remote control equipment for the searchlight aswell as to operate the searchlight. In accordance with the usual custom,the searchlight is not maintained in operation during those periods,commonly referred to as listening periods, when an attempt is being madeto detect and locate a sound source such. for example, as an airplane,and, therefore, the only power required is thatnecessary to operate thesound-locator apparatus and the remote control system for thesearchlight. Under such conditions, it is extremely important to operatethe power plant at a low or idling speed in order to reduce the noise toa minimum so that the sound locator system may function to the greatestadvantage. However, during such periods of quiet operation, it isnecessary to maintain the voltage of the power source substantiallyconstant at a value somewhere near the value at full load and to providefor automatically maintaining the voltage at the same value, or at somehigher value when the load increases as the result of initiating theoperation of the searchlight. Furthermore, it is very desirable tomaintain the generator voltage substantially constant over its operatingrange in order that the sound locator and remote control equipment aswell as the searchlight will function effectively.

Heretofore it has been the practice to utilize a power plant foroperating searchlights and the like in which the engine speed iscontrolled by means of a mechanical governor only. The low or idlingspeed is usually obtained by using a load responsive device or relay forrendering the governor ineffective to open the engine throttle for fullspeed operation and which functions upon a predetermined increase ingenerator load to release the governor. In some instances voltageregulators, acting upon the generator field winding, have also been usedto maintain the generator voltage substantially constant under varyingloads and at substantially constant engine speed.

It has been found that power plants of this type possess certaindisadvantages when used in connection with an arc searchlight whichconstia corporation of Penn- 1935, Serial No. 43,315 (Cl. 290-40) tutesa very unsteady load due to the fact that the arcmust be struck in orderto start the light,

and the carbons are continually burning away and being fed to the are.In other words the arc tends to lengthen and shorten which produces bothcurrent and voltage fluctuations which must be taken care of by thepower plant otherwise unsteady operation and flickering of the arc willresult. I

When power plants of the type described are used, and especially where avoltage regulator is used to control the excitation of the generator,the engine speed is limited to a predetermined maximum and the regulatortends to maintain the voltage at all times. In nearly all, if not all ofthe present day are searchlights, the electrode feeding mechanismsoperate with a certain amount of time lag or in other words some time isrequired to reestablish the desired arc condition when it varies. It isdesirable, therefore, if the best operation of the light is to beobtained, that the electrode feeding mechanism be pe mitted to functionas effectively as possible and that the power plant have suchcharacteristics as to permit this. When a mechanical governor andvoltage regulator are used, the power plant actually responds to voltagevariations in the arc before the feeding mechanism can respond theretowhich only aggravates the condition and makes it more difficult for thefeed mechanism to quickly and successfully restore the arc to its propercondition. This results in an unsteady arc and consequently, aninefficient and ineffective light.

In additionto the foregoing disadvantages,

power plants of this type have a limited overload capacity since theengine attempts to maintain a constant speed and can go no higher inorder to develop the necessary additional power. When a heavy load isapplied, such, for example, as when the arc is struck, the response ofthe power plant is so rapid that the engine is greatly overloaded andwith the voltage regulator attempting to maintain the voltage theoverload condition becomes worse which may stall or kill the engineunless a considerable amount of reserve power is provided.

I have found that all of these disadvantages may be successfullyovercome by utilizing a power plant in which the voltage is maintainedby controlling the engine speed, preferably in accordance with thegenerator load, and without the use of a mechanical governor except tolimit the maximum speed of the engine to a safe value.

-It is, therefore, .the object of the invention, generally stated, toprovide a power plant especially adapted for use with searchlightequipment and the like, which shall be of simple and reliable nature,eiiicient in operation and which may be economically manufactured andutilized. A more specific object of the invention is to providefor-automatically controlling the speed of an engine-generator set inaccordance with both the load and voltage of the generator to maintainconstant generator voltage under varying load conditions.

Another object of the invention is to provide for utilizingelectro-responsive means controlled in accordance with the generatorvoltage for controlling the fuel'control valve or throttle ofan internalcombustion engine driving the generator.

A still further object of the invention is to a provide for controllingthe speed of an engine driving a generator by means of anelectricallyoperated throttle control, in addition to a mechanicalgovernor throttle control for limiting the maximum engine speed,which'functions to maintain a low engine speed at light loads and ahigher or normal speed range above a predetermined load value and whichregulates the enerator set to produce a substantially constant generatorvoltage at all loads by means of an electrical governor which isresponsive to the generator load and which is controlled by a reg-'ulator responsive to generator voltage.

A still further object of the invention is to provide for regulating thespeed of an enginegenerator set by means of an electric throttle controlwhich functions to automatically maintain a predetermined generatorvoltage at low engine speed on light loads and to automatically vary theengine speed inaccordance with load demand.

' Another object of the invention is to provide for controlling thegenerator voltage of an engine driven generating unit by speed controlof the engine in order to provide relatively slow voltage response onsuddenly applied and varying load conditions and to provide'maximumoverload capacity with minimum engine capacity.

These and other objects of the invention will become apparent from thefollowing description of a preferred embodiment of the invention takenin conjunction with the drawing, in which the single figure is adiagrammatic view of an engine generator system embodying the principalfeatures of the invention.

In practicing the invention in the preferred .form, the power plantcomprises a generator having a drooping load characteristic driven by asuitable internal combustion engine. The generator and engine mayconstitute a unit or the generator may be mounted on a truck and thetruck engine utilized to drive it. The engine may be provided with amechanical governor to control one throttle valve in order to limit itsmaximum speed and which does not function in any way to control theengine speed in accordance with the generator load. The speed of theengine is controlled to maintain a desiredgenerator voltage by means ofan electric throttle control which functions to control a secondthrottle valve; The second throttle valve is biased toward its openposition by means of a spring and its closing movements are controlledby a torque motor or other suitable electro-responsive device which maybe responsive to generator load and which may be adjusted by means ofsuitable resistors to so regulate the engine speed as to main-.

tain any desired voltage. A regulator responsive to the generatorvoltage is utilized to further control the torque motor. The regulatoris controlled by means of a load relay in order to cause the generatorto maintain a predetermined voltage under light load conditions and toeffect an increase in voltage when the load increases to a predeterminedvalue, such for example, as when the searchlight is turned on. Thetorque motor or other electro-responsive device when controlled by thegenerator load current may be utilized alone to maintain approximatelyconstant voltage. When used in conjunction with the regulator the torquemotor need not be responsive to the generator load since its operationmay be controlled entirely 'by the regulator.

Referring now to the drawing, there is illustrated an engine generatorsystem for supplyingpower to a variable load such, for example, as asearchlight and the remote control and sound locator apparatus therefor.While the system is illustrated and described in connection withsearchlight equipment, it is to be understood that the principles of theinvention may be applied to power plants for other uses where it isdesired to maintain substantially constant voltage operation at widelyvarying loads and also under conditions where it is desirable tomaintain a lownoise level at certain times.

The searchlight load in this instance is illustrated by the carbonelectrodes l0 andv II and the auxiliary load l2 which may comprise theremote control system for the light and the necessary data transmittingsystems between the sound locator (not shown) and the remote controlstation or searchlight. Since the load apparatus IO H and I2 is not apart of this invention, it is deemed unnecessary to illustrate ordescribe them in detail.

The power plant in general comprises a direct-current generator 13 andan internal comfield winding is connected across the generator armatureterminals through a fieldrheostat i 9.

It will be readily understood that the use of a generator of this typemakes it possible to obtain a substantially constant generator voltageunder light load conditions with low engine speeds resulting in aminimum amount of noise and to maintain the same voltage or any otherdesired voltage substantially constant over the entire load range of theengine and generator by control of the engine speed.

The engine I4 is provided with a plurality of throttle valves 2| and 22positioned in the intake passage 23 for controlling the speed of theengine in the usual manner. The throttle valve 2| is controlled by meansof a mechanical governor 24, which in this instance functions only tolimit the maximum speed of the engine, and does not function in any wayto regulate the engine speed to maintain the generator voltage as theload varies. g

The regulation of the engine speed to maintain a desired generatorvoltage is effected in this embodiment of the invention by means of anelectrical throttle control comprising generally an electric governor 25and a voltageregulator 25. The electric governor 25 may take the form ofa torque motor, as shown, having an armature or movable element 21,which is connected to the throttle valve 22 in any suitable manner,such, for example, as by the plate 28 and rod 29. The armature of thetorque motor is normally maintained in the position shown by theadjustable springs 3| and 32, and is disposed, when energized, torotate, through a partial revolution, in a clockwise direction aslimited by the stop 33. 'Ihetorque motor is provided with a main fieldwinding 34 and an auxiliary field winding 35, for a purpose to bepresently described.

The voltage regulator 25 is of a well-known construction, and is fullydescribed in the United States Patent No. 1,820,712, granted to WalterSchaelchlin, on August 25, 1931. In general, this regulator comprises amagnetic circuit 35 and a movable element 31, which functions inconjunction with the adjustable spring 38 to actuate the movable contactelement 39 which vibrates between the adjustable stationary contactelements 4| and 42. The regulator is provided with a movable coil 43,a'stationary main coil 44 and an anti-hunting coil 45.

In this instance, the armature of the torque motor is connected acrossthe generator or load circuit represented by conductors l1 and I5 inseries with a torque motor resistor 48, its main field winding 34, themovable and stationary coils 43 and 440i the regulator, a variableresistor 49 and a load resistor 5| The torque motor armature is alsoconnected directly to the load conductor l5 through a variable resistor52, which is in parallel relation to the main field winding 34, theregulator coils and the resistors 49 and 5|. In order to cause theelectric governor 25 to regulate the engine speed in such manner as tomaintain the generator voltage, as the generator load varies, itsauxiliary field winding 35 is in the nature of a difierential field andis connected across the dlfi'erential series field winding l5 oi thegenerator through'a variable resistor 53. As will be readily understood,the excitation of the diiferential field 35 is automatically varied insuch a manner as the generator load varies as to cause the torque motorarmature to adjust itself to the required position to maintain thenecessary throttle setting.

The torque motor or electric governor 25, when connected in this manner,is capable 01' functioning alone to maintain the generator voltage atapproximately the desired value. However, in this instance, the voltageregulator 25 is utilized to further control the operation of the torquemotor to more accurately maintain the desired voltage. As shown, themoving contact element 39 of the regulator is disposed, when inengagement with the stationary contact 4|, to shunt the armature of thetorque motor through a variable resistor 54. The vibration of the movingcontact element, therefore, regulates the amount of current flowingthrough the torque motor armature in accordance with the voltageadjustment of the regulator.

anemone The back contact 42 oi the regulator is connected to the shuntfield winding l5 oi the generator and when engaged by the moving contactelement 33 shunts this field winding through the resistor 54 for thepurpose of preventing the overshooting of the generator voltage onremoval of load. The anti-hunt coil 45 of the regulator is connectedthrough a suitable resistance 55 across the contact elements 39 and 4|of the regulator and functions in the usual manner.

The setting of the voltageregulator 25 is controlled by the resistors 49and 5|. The efiectiveness of resistor 5| maybe controlled by the loadsetting switches 55 and 51 which may be opened or closed in difierentcombinations to cause the generator to maintain any desired voltage atdifferent load values. In this particular application, the Searchlight,or other load device, may operate at three difierent ampere ratings,such, for example, as at 150, 200 and 250 amperes. One value ofgenerator voltage for the ampere load may be obtained by closingswitches 55 and 51; another value obtained for the 200 ampere loadbyclosing switch 56 and leaving switch 51 open; and a still furthervalue of voltage obtained for the 250 ampere load by leaving bothswitches 55 and 51 open.

In this embodiment of the invention, provision is made for causing thegenerator |3 to maintain one value of voltage under light load operationand a diiierent value of voltage when the load exceeds somepredetermined value. This is accomplished by means of the load relay 5|having its operating winding connected across the series field winding|5 of the generator, and its contact members 52 connected to shunt theload resistor 5|. As will be apparent, when the generator load is belowthe-value for which the load relay 5| is adjusted, a large portion ofthe resistor 5| is shunted which causes the regulator to maintain apredetermined voltage regardless of the position of the load switches 55and 51. Upon operation of the load relay, the load switches 55 and 51become efifective to control the regulator setting The functioning ofthe torque motor may be controlled or adjusted by the resistors 45 and52 in its armature circuit, the variable resistor 53 in its fieldcircuit, and the adjustable spring elements 3| and 32 which function tonormally bias the throttle 22 toward the open position.

While in this instance the electric governor 25 is rendered responsiveto the generator load current by means of its differential field winding35, it will be apparent that such is not necessary since the regulator25 may be utilized to control its operation independently oi thegenerator load if desired. The connections shown,

however, are such as to impose a lighter duty on the regulator since theelectric governor 25 inherently functions to approximately maintain adesired generator voltage under all load conditions and the regulator 25is only required to correct the setting of the electric governor to moreaccurately maintain the generator voltage at the desired value.

In order to reduce the noise level of the plant to as low a value aspossible, provision is also made for driving the cooling fan 53 for theradia tor 54, when such is used, by means of a seperate motor 55, thespeed of which may be controlled in accordance with the engine orgenerator load to give the desired amount of cooling under both lightand heavy load operation.

In this instance, the fan motor 55 is connected across thegenerator loadconductors l1 and I8 in series with a resistor '66 which functions tocontrol the fan motor speed. The efiectiveness of the resistor 66 may beconveniently controlled I by the load relay iii, the contact members 61thereof being disposed to shunt the resistor 66 and increase the motorspeed when the relay operates at the predetermined load value.

With this arrangement the fan motor 65 operates at a low speed duringlight load operation, or during the listening period, when the powerplant is being used with searchlight apparatus. Aside from the reductionin noise the engine 14 is maintained at its normal operatingtemperature, providing smoother operation and a warmed up engine whichis always in a condition to assume full load. Furthermore, since theengine is always operated at normal temperature, it stays in betteroperating condition,

and consequently, may be operated on light loads over long periodsoftime without mechanical attention.

In view of the foregoing description, it is apparent that the inventionprovides a greatly improved form of throttle control for internalcombustion engines which is of extremely simple and rugged nature andwhich is capable of functioning to so regulate the engine speed that thegenerator voltage will be maintained substantially constant regardlessof load variations over the entire operating range of the machine. Theelectric throttle control functions independently of the mechanicalgovernor, and thus requires no readjustment or resetting as thegenerator load increases. It functions also to maintain a low idlingspeed of the engine, and consequently a low noise level when thegenerator load is small, and performs without further adjustment to takecare of increased generator load.

It is further apparent that this power plant embodies highly desirablefeatures and advantages not present in power plants now in use. Theprinciple of controlling the generator voltage by speed control of theengine is highly desirable, since it provides a relatively slow voltageresponse which is a distinct advantage where the power plant issubjected to widely varying and suddenly applied loads and also when theload device is of such nature that it must be permitted to functionproperty without interference on the part of the power plant operation,such, for example, as in the case of an arc searchlight. Control of thegenerator voltage by controlling the engine speed, as distinguished froma form of control wherein the generator voltage is controlled by aregulator acting upon its field winding, enables the engine to readilypick up a suddenly applied load, such as results when the arc is struck,and furthermore, enables the generator voltage to follow the operationof the arc controlling mechanism and not precede it. The are controlmechanism is thus permitted to perform its function without interferencefrom the generator which results in a marked increase in the steadinessof the operation of the searchlight.

illustrated example constitutes a practical embodiment of my invention,I do not wish to limit myself strictly to the exact details hereinillustrated, since modifications of the same may be made withoutdeparting from the spirit of the invention defined in the appendedclaims.

I claim as my invention:

1. In combination, a generator, an engine for driving the generator,electro-responsive means for controlling the speed of the engine inaccordance with the generator load, and a separate regulator deviceresponsive to the generator voltage for controlling the energization ofsaid electro-responsive means in accordance with the voltage of thegenerator to maintain substantially constant generator voltageregardless of varia tions in generator load.

2. In combination, a generator, an engine having a fuel control valvefor driving the generator, a torque motor connected to actuate the fuelvalve and responsive to generator load for controlling the speed of theengine, and a vibratory regulator for further controlling the operationof the torque motor to cause the generator to develop substantiallyconstant voltage as the generator load varies.

3. In combination, a generator, an engine for driving the generator,electro-responsive means for controlling the speed of the engine,voltage regulator means responsive to the generator voltage forcontrolling said electro-responsive means to maintain a substantiallyconstant generator voltage, and means responsive to a predeterminedincrease in generator load for causing said voltage regulator means toefiect an increase in the generator voltage.

4. In a power plant, in combination, a generator, an engine for drivingthe generator, means including a torque-motor for controlling the speedof the engine, and means responsive to a predetermined generator loadfor rendering said means including the torque-motor efiective to producea predetermined increase in the generator voltage.

a regulator responsive to generator voltage for controlling the flow ofcurrent through the torque-motor, thereby to maintain a substantiallyconstant generator voltage.

6. In a power plant for supplying electrical power to a variable loadcomprising a direct-current generator, an internal combustion engine fordriving the generator, an electrical governor having field. and armaturewindings for controlling the engine speed to cause the generator tomaintain approximately a desired voltage, said field winding beingexcited in accordance with the generator load and a voltage regulatorfor controlling the. armature current of the electrical governor,whereby the generator voltage is maintained at a substantially constantvalue regardless of load variation.

'7. In a power plant for supplying electrical power to a variable loadcomprising a direct-current generator, an internal combustion engine fordriving the generator, an electrical governor responsive to generatorload current for controlling the engine speed to cause the generator tomaintain approximately a desired voltage, a voltage regulator forfurther controlling the operation of the electrical governor to providesubstantially constant generator voltage, and means responsive to apredetermined increase in generator load for changing the adjustment ofthe regulator to produce a higher generator voltage, whereby the speedof the engine is so regulated as to cause the generator voltage to bemaintained substantially constant at different values over differentload ranges.

8. An engine-generator unit for supplying power to a varying load atconstant voltage, comprising a generator having a droopingcharacteristic, an engine for driving the generator, means including atorque motor for controlling the speed 01' the engine, said torque motorbeing responsive to variations in the generator load to vary the enginespeed in accordance with load variation of the generator toapproximately ,maintain a desired voltage, and a separate regulatordevice responsive to generator voltage for controlling the armaturecurrent-of the torque motor, thereby to cause the engine speed to be ad-Justed to maintain substantially constant generator voltage undervarying load conditions.

9. A power plantfor' supplying power to a variable load comprising agenerator, an internalcombustion engine for driving the generator, saidengine being provided with a plurality of fuel control valves,aspeed-responsive governor for controlling one of said valves to limitthe maximum speed of the engine, electro-responsive means jointlyresponsive to the generator load current and voltage for controlling theother valve, and means for adjusting said electro-responsive means tocause the generator to maintain different predetermined voltagesregardless of load variation.

10. A power plant for supplying power to a variable load comprising adiilEerentially-compounded generator, an internal-combustion engine fordriving the generator, said engine being provided with a plurality offuel control valves, 9. speed-responsive governor for controlling one ofsaid valves to limit the maximum speed of the engine, electro-responsivemeans jointly responsive to the generator load current and voltage forcontrolling the other valve, means for adjusting said electro-responsivemeans to cause the generator to maintain different predeterminedvoltages regardless of load variation, and load responsive means forcontrolling the functioning oi the electro-responsive means, thereby tocause the generator to maintain one voltage below a predetermined loadand another voltage above said predetermined load.

11. A power plant for supplying power to a.

variable load comprising, a generatorhaving a drooping characteristic,an engine for driving the generator, electro-responsive means Jointlyresponsive to the voltage for controlling the speed of the engine tomaintain a desired generator voltage, and means responsive to apredetermined generator load for causing said electro-responsive meansto function to increase and maintain a difl'erent generator voltage.

12. A power variable load comprising a diil'erentially-compoundedgenerator, an engine for driving the generator, an electro-responsivedevice ior controlling the speed of the engine in accordance with thegenerator load, regulator meansresponsive to the generator voltage forcontrolling the electroresponsive device, resistor means for varying thecalibration oi the electro-responsive device and regulator means todetermine the generator voltage, and relay means for controlling theeil'ectiveness of the resistor means, said relay means being disposed tonormally render the electro-responsive device and regulator meanseffective to maintain one predetermined generator voltage and operableat a predetermined generator load for rendering saidelectro-responsivedevice operable to maintain another predetermined generator voltage.

13. A power plant for supplying power to a variable load comprising agenerator, an engine for driving the generator, a torque motor forcontrolling the speed having difl'erentially-related field windings oneof which is responsive to the generator load current to increase theengine speed as the load increases, a regulator operable to shunt thearmature oi the torque motor and having an operating coil connected inseries with the torque motor, and variable resistance means forcontrolling the functioning or the regulator to determine the generatorvoltage. 1

14. A power plant for supplying power to a variable load comprising agenerator, an engine for driving the generator, a torque motor forcontrolling the speed of the engine, said torque motor havingdlflerentially-related field windings one 01 which is responsive to thegenerator load current to increase the engine speed as the loadincreases, a regulator operable to shunt the armature or the torquemotor and having an operating coil connected in series with the torquemotor, variable resistance means for controlling the functioning oi theulator to determine the generator voltage, and means responsive togenerator load current for varying the effectiveness of the resistormeans, whereby the generator maintains difi'erent voltages dependentupon the load.

LEO C. FRANK.

or the engine, said torque motor generator load current and plant forsupplying power to a

